1. Field of the Invention
The invention relates to a radiation-sensitive resin composition, a method for forming a resist pattern, and a polymer.
2. Discussion of the Background
In the field of microfabrication such as production of integrated circuit devices, a fine resist pattern is formed by forming a resist film on a substrate using a resin composition including an acid-dissociable group-containing polymer, exposing the resist film by applying short-wavelength radiation (e.g., excimer laser light) to the resist film via a mask pattern, and removing the exposed area using an alkaline developer. This process may utilize a chemically-amplified resist that includes a photoacid generator that generates an acid upon irradiation, and exhibits improved sensitivity due to the acid.
Liquid immersion lithography has become widespread as a method that forms a finer resist pattern having a line width of about 45 nm using the chemically-amplified resist. According to liquid immersion lithography, the resist film is exposed in a state in which the exposure optical path (i.e., the space between the lens and the resist film) is filled with an immersion medium (e.g., purified water or fluorine-containing inert liquid) that has a refractive index (n) higher than that of air and inert gas. Therefore, the depth of focus decreases to only a small extent, and high resolution can be obtained even if the numerical aperture (NA) of the lens is increased.
A resin composition used for liquid immersion lithography is required to prevent a decrease in film performance and contamination of the apparatus (e.g., lens) by suppressing elution of the acid generator and the like from the resist film into the immersion medium, and make it possible to implement high-speed scan exposure by preventing a situation in which watermarks remain through an improvement in draining capability of the surface of the resist film. For example, Japanese Patent Application Publication (KOKAI) No. 2005-352384 discloses technology that forms an upper-layer film (protective film) on the resist film in order to deal with such a demand. A method that improves the hydrophobicity of the surface of the resist film has been examined. For example, WO2007/116664 discloses a resin composition that contains a fluorine-containing polymer having high hydrophobicity. Japanese Patent Application Publication (KOKAI) No. 2008-268931 discloses technology that introduces an alkali-soluble unit in a fluorine-containing polymer.